1. Field of the Invention
The present invention relates to a systems and methods for positioning optical components within a lithographic apparatus.
2. Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., comprising part of, one, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging the pattern using a UV radiation beam onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
In such lithographic apparatus, it may be necessary to control accurately the position of one or more optical components, such as those optical components within an illumination system configured to condition a radiation beam, or those optical components within a projection system configured to project a patterned radiation beam onto a substrate. Therefore, lithographic apparatus often incorporate an actuator system that accurately positions an optical component of the lithographic apparatus relative to one or more additional optical components of the lithographic apparatus.
Further, existing actuator systems generally position optical components within the lithographic apparatus as accurately as possible. These existing actuator systems often incorporate individual actuators that exhibit high levels of stiffness, thereby maximizing an accuracy of a response of the optical component to the actuation mechanism. For example, existing actuator systems may incorporate piezo-actuators, which exhibit relatively high stiffness.
However, the overall stiffness of existing actuator systems may not be as high as the stiffness of the individual actuators. For example, each actuator may be associated with a mechanical decoupling mechanism that ensures the system is stiff only in the driven direction and not in other directions, such as rotational directions. Although these mechanical decoupling mechanisms are necessary in order to avoid mechanical deformations during use of the actuator systems, these mechanical decoupling mechanisms may result in a significant decrease in the stiffness of the connection of the actuator to the optical component. For example, a piezo-actuator used to control the position of an optical component may have a stiffness of 200 N/μm, while the decoupling mechanism may only have a stiffness of 120 N/μm. In this case, the combined stiffness of the connection of the piezo-actuator to the optical component is only 75 N/μm, resulting in a reduced performance of the actuator system.